PCDD AND PCDF LEVELS IN RIVER SYSTEMS IN ENGLAND AND WALES, UK

Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) are present naturally in the environment, but these natural sources are of relatively little importance compared with the emission of PCDD/Fs into the environment as unwanted by-products of anthropogenic processes. This study was initiated by the UK National Rivers Authority (NRA) with the overall objective of determining the distribution of PCDD/Fs in surface freshwaters of England and Wales. The study involved the collection of surface waters and associated deposited sediments from a number of rivers in England and Wales. These included both potentially contaminated and background sites. In all, water was sampled from 40 sites with associated deposited sediments successfully sampled at 36 of these. The shortfall in the latter reflected the scarcity of deposited sediment at some locations. Where potential point sources of PCDD/Fs were identified, samples were taken upstream and downstream of these locations. The concentrations in the water samples were extremely low, with a total concentration (defined as total PCDD/Fs with 4 or more chlorine substitutions) of <6 ng l(-1), and an International Toxic Equivalent (I-TEQ) of <0.08 ng l(-1). PCDD/Fs were detected in all the deposited sediment samples, and total PCDD/F concentrations and I-TEQ values varied considerably between sites (300 - 16 000 ng kg(-1) total concentration, 2-120 ng kg(-1) I-TEQ). There are little comparative data available on PCDD/F concentrations in UK rivers, but the sediment results from this study are comparable to the PCDD/F range found in UK soils, and in surface river sediments measured elsewhere in Europe.